1. Field of the Invention
The present invention relates to a process for the preparation of low density composite laminate structures consisting of a bismaleimide-glass laminate face sheets adhered to a bismaleimide honeycomb structure containing carbon microballoons bonded with bismaleimide resin. Panels and structures prepared in accordance with the present invention are useful as aircraft panels and panels for vessels which require high ignition temperature and minimum of gassing and evolution of noxious and toxic fumes upon ignition.
2. Description of the Prior Art
Panels and structures employed by manufacturers as the interior paneling of aircraft and vessels subject to confined or constricted environments have generally employed glass-epoxy resins combined with a polyamide core. The prior art structures due to the presence of epoxy exhibit large smoke evolutions and a low fire containment capacity when subjected to heat or flame.
In general the panels and aircraft lining structures have been prepared by silk screening the required decorative surface on a 0.005 cm polyvinyl fluoride film (Tedlar) by a continuous web process. After drying, a 0.0025 cm transparent polyvinyl fluoride film coated on one side with polymethyl methacrylate is bonded to the decorative film to provide protection for the printed surface.
The laminate is then bonded to one ply of epoxy-preimpregnated 181E glass, and may have a surface texture imposed during the bonding operation.
One core material presently employed for sandwich paneling is an aromatic polyamide (sold under the tradename Nomex HRH-10) hexagonal-cell honeycomb structure. The cell size may be 0.312 cm, 0.625 cm, or 0.937 cm, depending upon the properties desired in the finished panel.
The prior art method of binding an outer panel to the core consists of using an epoxy resin-preimpregnated bond ply over which is applied the prepared glass/polyvinyl fluoride decorative laminate. The resin in the bond ply provides the adhesive to bond the outer panel to the honeycomb and the decorative laminate to the bond ply. Curing is accomplished at 110.degree. C. with 50 cm Hg minimum vacuum bag pressure. For a panel requiring a decorative laminate on one side only, a bond ply is used as the outer panel on the other or back side.
Structures and panels prepared in accordance with the prior art have exhibited relatively lower fire containment capabilities because of the absence of insulative material in the honeycomb core. The prior art structures also evolve large quantities of smoke and toxic fumes when exposed to fire or heat due to the presence of the epoxy material and the glass-epoxy resinous substrate.